Process for forming lead pellets



Jan. 10, 1967 C. JACKLIN ETAL PROCESS FOR FORMING LEAD PELLETS Filed Aug. 19, 1965 BOILING WATER OR A VISCOUS LIQUID OR A LIQUID OF LOW THERMAL CONDUCTIVITY INVENTORS: CLAR ENCE JACKLI N PETER L GROSS United States Patent 3,297,799 PROCESS FOR FORMING LEAD PELLETS Clarence Jacklin, Downers Grove, and Peter L. Gross, Riverside, Ill., assignors to Nalco Chemical Company, Chicago, 11]., a corporation of Delaware Filed Aug. 19, 1965, Ser. No. 483,017 8 Claims. (Cl. 264-14) The present application is a continuation-in-part of application Serial No. 120,762 which was filed on June 29, 1961.

The present invention relates to a process and apparatus for forming lead pellets. More particularly, the invention is directed to a process and apparatus for forming lead pellets having smooth surfaces,'which pellets are satisfactory for use in mostcommercial operations.

In the conventional method of forming lead pellets molten beads of lead are dropped from shot towers into quenching tanks. The height of such towers generally is from about 85 to 125 feet. The beads solidify in the air before entering the quenching liquid. Towers of this type were used in order to form pellets having desirable shapes and smooth surfaces. Although such shot towers produce satisfactory pellets, this equipment takes up a considerable amount of space and represents a substantial capital outlay. H I Y The principal object of the present invention is to provide a process for forming satisfactory lead pellets which process can be carried out in compact and relatively inexpensive equipment.

Other objects will become apparent to those skilled in the art from the following description of the invention.

In general, the invention comprises the discovery that satisfactory pellets can be formed by passing drops of lead from a dispensing means through air for a distance of from about 1 to about 6 inches and even as low as /2 inch into particular quenching agents. Our preferred drop distance is from 1 or IV: inches to 3 inches. The distance between the dispensing means and the quenching agent is important to the success of the invention as is the nature of the particular quenching liquid.

It was discovered that satisfactory lead pellets can be formed after a drop of only a few inches if the quenching material is such that an immediate solidification of the pellet does not take place. In particular, it was found that if means were provided for protecting the pellet against instant solidification a substantially spherical and smooth pellet could be obtained.

The necessary delay in the solidification of the pellets on entering the quenching liquid can be achieved by any one of three methods. The first of these methods is to drop the pellets into water which is actively boiling. It was found that on striking the water a film of steam is formed around the pellet which prevents immediate solidification. The second method is to drop the pellets into liquids having particular viscosity characteristics. Like boiling water, such liquids appear to form a protective film of vapor and/or liquid around the pellet. This protective film acts to retard the solidification of the pellet. The third method and preferred method of providing a relatively gradual solidification is to drop the pellets into quenching liquids having particular thermal conductivity characteristics. Water conducts heat rapidly and, therefore, it is not a satisfactory cooling agent unless it is actively boiling. Products such as hexylethyl Carbitol (diethylene glycol ethyl hexyl diether) and the diethyl ether of tetraethylene' glycol, however, do not conduct heat rapidly. For this reason the rate of solidification of the lead pellets is slowed and a smooth and relatively spherical product can be obtained.

It has been found that the distance between the outlet opening of the drop-forming means and the quench 3,297,799 Patented Jan. 10, 1967 "ice liquid should be between about 1 to 6 inches. Preferably, this distance will be from about 1 /2 to 3 inches. If this distance is greater than 6 inches, the drops tend to splatter on striking the liquid. The form assumed by the pellet on solidification under such circumstances is not satisfactory.

If the second method of retarding the solidification of the pellets is employed, the liquids should have a viscosity of from about 500 to about 5,000 Saybolt seconds and preferably from about 1,000 to about 3,000 Saybolt seconds. Water-insoluble and water-soluble polyalkylene glycol liquids having these characteristics can be used as the quench medium.

The quenching tank can be of any desired shape. It has been found, however, that liquid within the tank should have a depth of at least about 12 inches. If the depth is less than 12 inches the pellets often smash against the bottom of the tank causing them to lose their spherical shape. In a preferred embodiment the liquid within the tank is from about 2 to about 4 feet deep.

The upper limit with respect to the depth of the liquid,

of course, is unimportant insofar as the success of the process is concerned.

The attached drawing schematically sets forth certain equipment which can be used to carry out the present invention.

FIGURE -1 is a sectional view of a complete pelletforming device; s 7

FIGURE 2 is a sectional view of a drop dispensing unit;

FIGURE 3 is a front view of a flow control means which is used to regulate the rate at which the lead drops from the dispensing means; and

FIGURE 4 is a front view of a dispensing pipe containing multiple dispensing units.

In FIG. 1 lead 1 within pot 2 is maintained in a molten condition by means of heating mantle 3 which is powered by variable transformer 4. Dial thermometer 5 is used to maintain a check on the temperature of the lead. The lead passes from pot 2 through pipe nipple 6 and out a V-notch. The rate of flow of the drops of lead through the V-notch is controlled by means of screw 7. The drops of lead leaving pipe nipple 6 through the V-notch fall a specific distance into quench liquid 8 which is maintained within quench vessel 9. Stirrer 10 circulates the liquid within the vessel. The temperature of the cooling liquid is controlled by means of cooling unit 11 which consists of inlet pipe 12 and outlet pipe 13. Valve 14 controls the flow of water through cooling unit 11.

An expanded cross-sectional view of nipple 6 is shown in FIG. 2. Outlet opening 15 was tapped for a 10-24 round head screw. V-notch 16 is cut into pipe nipple 6 to provide a means for dispersing lead drops at a desired rate. The threads on the upper half of screw 7 are filed away to allow the lead drops to pass through the V- notch. When the screw is tight the end of the nipple is leakproof. As the screw is loosened the molten lead begins to flow through the recessed portion of the screw thread and escapes around the screw head. This device provides a uniform and easily controlled flow of lead. If desired, the V-notch could be made in the unfiled threads rather than in the nipple. Nipple 6 is removably mounted in sleeve 17 of pot 2.

FIG. 3 is an expanded front view of the dispensing unit of FIG. 2. V-notch 16 has been cut into the end of nipple 6. The head of screw 7 covers the opening of the nipple when the screw is tight. As the screw is loosened, the filed portion of the threads of the screw allow lead to flow out around the head of the screw whereupon the formed drops fall into quench liquid 8.

Example I In this example a dispersing unit similar to that setforth in FIG. 1 of the drawing was used to produce pellets. The quenching liquid consisted of hexylethyl Carbitol (diethylene glycol ethyl hexyl diether). A series of tests were made using hexylethyl Carbitol wherein the fall distance was varied between 1% inches and 3 /2 inches. The results of the tests were as follows:

TEMPE RATURE OF MOLTEN LEAD Fall 690 F. 720 F. Distance 1% in Uniform tear drop shape Unliforin short tear drop s tape. 2% 1'n Smooth uniform short tear Uniform short tear drop drop shape (Good). drop shape (Good). 3 in Same as above but; not Longer points on tear drop quite as smooth. than above. 3% in Same as above Lting gaar drop (Low Pb eve Comparable results are obtained using other Carbitols such as diethyl ether of tetraethylene glycol.

Example II In this example the pellets were dripped from a single drop unit into boiling water. The fall distance was 1 /2 inches and the drop rate was about 5 per second. The diameter of the opening in the nipple was 0.04 inch. The temperature of the molten lead was 660 F., and the depth of the water in the quench tank was 50 inches. It was found that this process produced uniform, smooth, and substantially spherical shaped pellets.

Although the size of the pellets produced by the subject process can vary widely in accordance with the use to which they are to be put, such pellets usually have a diameter of from about A to about W of an inch. The outlet openings of the drop dispenser will vary according to the size of the pellet which is desired. Openings of from about 0.025 to about 0.1 inch in diameter have been found to be satisfactory for most purposes.

As was indicated above, the quench liquid should be either (1) boiling water, (2) a liquid having a viscosity of from about 500 to 5,000 Saybolt seconds, or (3) a liquid having particular heat conductivity properties. Hexylethyl Carbitol (diethylene glycol ethyl hexyl diether) and diethyl ether of tetraethylene glycol are examples of liquids which fall into the latter category. Other suitable liquids include other Carbitols :as well as Cellosolve and other hydroxy ethers having the general formula where R is a lower alkyl radical having from 1 to 4 carbon atoms or a phenyl group, and x is 1 or 2. Carbitols having the general formula wherein R and R are members selected from the group consisting of alkyls having 1 to 6 carbon atoms and benzyl and wherein n is a whole number from 1 to 6 are suitable.

Water-insoluble and water-soluble polyalkylene glycols can be used as the quench medium. One such product which is water-insoluble is commercially available under the trademark Ucon Lubricant LB1715, while a watersoluble polyalkylene glycol is sold under the trademark 4 Ucon Lubricant 50 1-18-5100." The Ucon type compounds are described in US. patent to Toussant et al., 2,425,845, which patent is incorporated in this application by reference.

The present invention provides significant advantages over the prior art methods. Acceptable lead pellets having smooth surfaces can now be obtained with a fall distance of from about 1 to 6 inches Without the use of shot towers which have a height of feet or more.

Our preferred quench liquids are hexylethyl Carbitol and diethyl ether of tetraethylene glycol. It has been found that this material not only provides a suitable means of retarding solidification of the lead pellets but also protects the pellets from oxidative deterioration. For this reason it is not necessary to provide other means for protecting the pellets after they have been formed.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for preparing lead pellets which comprises: dripping molten lead from a dispensing means into a quench liquid arranged beneath said dispensing means, the distance between said dispensing means and the surface of said quench liquid being from about 1 to 6 inches, said quenching liquid being selected from the group consisting of boiling water, polyalkylene glycols having a viscosity of from about 500 to about 5,000 Saybolt seconds, Carbitols having the formula wherein R and R are members selected from the group consisting of alkyls having 1 to 6 carbon atoms and benzyl and wherein n is a whole number from 1 to 6, and bydroxy ethers having the formula where R is selected from the group consisting of a lower alkyl radical having from 1 to 4 carbon atoms and a phenyl radical, and x is a whole number from 1 to 2.

2. A process for preparing lead pellets which comprises: dripping molten lead from a dispensing means into a quench liquid arranged beneath said dispensing means, the distance between said dispensing means and the surface of said quench liquid being from about 1 /2 to about 3 inches, said quenching liquid being selected from the group consisting of boiling water, polyalkylene glycols having a viscosity of from about 500 to about 5,000 Saybolt seconds, Carbitols having the formula wherein R and R are members selected from the group consisting of alkyls having 1 to 6 carbon atoms and benzyl and wherein n is a whole number from 1 to 6, and hydroxy ethers having the formula where R is selected from the group consisting of a lower alkyl radical having from 1 to 4 carbon atoms and a phenyl radical, and x is a whole number from 1 to 2.

3. A process for preparing lead pellets which comprises: dripping molten lead from a dispensing means into a vessel containing hexylethyl Carbitol, the distance between the exit opening of said dispensing means and the surface of said hexylethyl Carbitol being from about 1 to about 6 inches.

4. A process for preparing lead pellets which comprises: dripping molten lead from a dispensing means into a vessel containing hexylethyl Carbitol, the distance between the exit opening of said dispensing means and the surface of said hexylethyl Carbitol being from about 1 /2 to about 3 inches.

5. A process for preparing lead pellets which comprises: dripping molten lead from a dispensing means into a vessel containing boiling water, the distance between the exist opening of said dispensing means and the surface of said boiling water being from about 1 to about 6 inches.

6. A process for preparing lead pellets which comprises: dripping molten lead from a dispensing means into a vessel containing boiling Water, the distance between the exist opening of said dispensing means and the surface of said boiling Water being from about 1 /2 to about 3 inches.

7. A process for preparing lead pellets which comprises: dripping molten lead from a dispensing means into a vessel containing diethyl ether of tetraethylene glycol, the distance between the exit opening of said dispensing means and the surface of said diethyl ether of tetraethylene glycol being from about 1 to about 6 inches.

8. A process for preparing lead pellets Which comprises: dripping molten lead from a dispensing means into a vessel containing diethyl ether of tetraethylene glycol,' the distance between the exit opening of said dispensing means and the surface of diethyl ether of tetraethylene glycol being from about 1 /2 to about 3 inches.

References Cited by the Examiner UNITED STATES PATENTS 2,919,471 1/1960 Hechinger 26413 ROBERT F. WHITE, Primary Examiner.

J. A. FINLAYSON, Assistant Examiner. 

1. A PROCESS FOR PREPARING LEAD PELLETS WHICH COMPRISES: DRIPPING MOLTEN LEAD FROM A DISPENSING MEANS INTO A QUENCH LIQUID ARRANGED BENEATH SAID DISPENSING MEANS, THE DISTANCE BETWEEN SAID DISPENSING MEANS AND THE SURFACE OF SAID QUENCH LIQUID BEING FROM ABOUT 1 TO 6 INCHES, SAID QUENCHING LIQUID BEING SELECTED FROM THE GROUP CONSISTING OF BOILING WATER, POLYALKYLENE GLYCOLS HAVING A VISCOSITY OF FROM ABOUT 500 TO ABOUT 5,000 SAYBOLT SECONDS, CARBITOLS HAVING THE FORMULA 